| It may have a radius about 2.4 times that of our home planet, but NASA scientists have confirmed that Kepler-22b — depicted in the artist's conception up top — is the first planet we've ever confirmed orbits within the so-called "habitable zone" of a Sun-like star, making it the most Earth-like planet we've yet discovered. In astronomy, the habitable zone (also known as the Goldilocks zone") is the region surrounding a star in which an orbiting planet could maintain liquid water (and, by extension, life) on its surface. And as the "Goldilocks" moniker implies, whether or not a planet resides inside a habitable zone has everything to do with whether the planet is a little too cold, a little too hot, or just right, temperature-wise. Take Kepler-21b, for example, whose discovery was announced last week by the National Optical Astronomy Observatory. Kepler-21b is even closer to the size of Earth than Kepler-22b, but it orbits far too close to its sun to sustain any form of life we're familiar with; as this conception of K-21b by artist Ron Miller clearly illustrates, surface temperatures on the planet are estimated to reach as much as 3000-degrees Fahrenheit — that's hot enough to melt iron, not to mention any hope of us ever calling K-21b "Earth 2.0." But Kepler-22b is a different story. Sure, the planet orbits about 15% closer to its star than Earth does to the Sun, but its star is also significantly cooler, dimmer, and smaller than ours. And while scientists have yet to ... |
